Hacking: The Art of Exploitation

Hacking (English verb to hack, singular noun a hack) refers to the re-configuring or re-programming of a system to function in ways not facilitated by the owner, administrator, or designer. The term(s) have several related meanings in the technology and computer science fields, wherein a "hack" may refer to a clever or quick fix to a computer program problem, or to what may be perceived to be a clumsy or inelegant (but usually relatively quick) solution to a problem, such as a "kludge".
The terms "hack" and "hacking" are also used to refer to a modification of a program or device to give the user access to features that were otherwise unavailable, such as by circuit bending. It is from this usage that the term "hacking" is often used to refer to more nefarious criminal uses such as identity theft, credit card fraud or other actions categorized as computer crime. Hacks are usually achieved by a flaw found in the software. These flaws allow code to be built around using reverse engineering. Hacks that allow complete device modification allow Homebrew applications and Games to be played easily. Piracy is a problem that occurs when hacks are achieved. Using Hacks voids warranty and should only be done if you are completely sure its something you want. Be careful of what you do. Hacks that are downloaded from the internet may contain malware. Be sure to hack a Anti-Virus active before you download anything off the internet.

A hack could be anything from a simple icon modification to a full device overhaul.

Basically anything that was not intended for the device to do.